About six months ago I switched from Outlook to Gmail's web client for all my email. About the only hitch I have encountered so far is the five email account limit. As a computer geek I maintain several accounts for various reasons one of which is that it is a way to foil spammers.
But one thing that until recently bothered me was the fact that I could not just click on a link from a web site and pop up a new email window. When you encounter a generic problem like this there is a pretty good chance that someone has produced a extension that overcomes the limitation and sure enough programmers at Google have already created something called Send from Gmail which pops up a new window with the email address filled in and ready to go. Doing the same thing from a windows app still requires an external app but one is available in windows Vista. I wouldn't be surprised if this changes soon and even desktop apps will show up in the browser.